1. Field of the Invention
One embodiment of the present invention relates to a light-emitting device utilizing electroluminescence. Further, an embodiment of the present invention relates to an electronic device using the light-emitting device.
2. Description of the Related Art
In recent years, research and development have been extensively conducted on light-emitting elements including electroluminescence (EL). In a basic structure of such a light-emitting element, a layer including a light-emitting substance is provided between a pair of electrodes. By voltage application to this element, light emission can be obtained from the light-emitting substance.
Since the above light-emitting element is a self-luminous type, a light-emitting device using this light-emitting element has advantages such as high visibility, no necessity of a backlight, low power consumption, and the like. Further, such a light-emitting element also has advantages in that the element can be formed to be thin and lightweight and that response time is high.
The light-emitting device having the light-emitting element can have flexibility and impact resistance in addition to its thinness and lightness and thus has been expected to be applied to a flexible substrate. The light-emitting element is applied not only to the light-emitting device but also to a semiconductor device or the like which functions by utilizing semiconductor characteristics.
As a method for manufacturing a semiconductor device including a flexible substrate, a technique in which after a semiconductor element such as a thin film transistor is formed over a base material such as a glass substrate or a quartz substrate, the semiconductor element is transferred from the base material to another base material (for example, a flexible base material) has been developed. In order to transfer the semiconductor element to the another base material, a step for separating the semiconductor element from the base material that is used in forming the semiconductor element is necessary.
For example, a separation technique using laser ablation is described in Patent Document 1 as follows. A separation layer formed using amorphous silicon or the like is formed over a substrate, a layer to be separated which is formed using a thin film element is formed over the separation layer, and the layer to be separated is bonded to a transfer body with the use of a bonding layer. The separation layer is ablated by laser irradiation, so that separation is generated in the separation layer.
In addition, a technique in which separation is conducted by physical force such as human hands is described in Patent Document 2. In Patent Document 2, a metal layer is formed between a substrate and an oxide layer and separation is generated at an interface between the oxide layer and the metal layer by utilizing weak bonding between the oxide layer and the metal layer at the interface, so that the layer to be separated and the substrate are separated from each other.
Further, in Patent Document 2, an interlayer insulating film is formed over a light-emitting element including an anode, an organic light-emitting layer, and a cathode, and the interlayer insulating film is bonded to a supporting member with the use of a bonding layer. Then, separation is performed at the interface between the oxide layer and the metal layer, and the layer to be separated including the light-emitting element is bonded to a film substrate using the bonding layer, so that a light-emitting device using a flexible substrate is manufactured.
In addition, a display device provided with a touch sensor has attracted attention. The display device provided with a touch sensor is called a touch panel, a touch screen, or the like (hereinafter also referred to simply as a touch panel). A touch panel is used mostly in personal computers or cellular phones and allows image display and operation to be done on the same panel. Further, a display device provided with an optical touch sensor is disclosed in Patent Document 3.